1. Field of the Invention
The present invention relates to a structure of a semiconductor device and a manufacturing method thereof, and more particularly to, in a damascene process using a low dielectric film having a bond of Si and a group made of organic constituents, such as MSQ, an interface structure of a barrier metal and the low dielectric film and a surface treatment method thereof.
2. Description of the Related Art
To meet the high integration of a semiconductor device and a reduction in chip size in recent years, not only the miniaturization of the wiring, but also the multi-level interconnection is being promoted. As a method of forming a multi-level interconnect structure, a so-called damascene process is generally performed, by which an interconnect is formed by embedding Cu in both a via hole and a wiring trench pattern concurrently followed by planarization through the CMP (Chemical Mechanical Polishing) method. The damascene process can increase density of wiring patterns; however, when the wiring patterns are formed too close, a parasitic capacitance between the wiring patterns causes problematic interconnect delay. Hence, a reduction in interconnect capacitance becomes an issue of great importance to improve the interconnect delay.
In order to reduce the interconnect capacitance, there has been discussed a method of using a low dielectric material for the interlayer insulation film instead of a conventionally used SiO2-based insulation film. The conventional damascene process using a low dielectric film as the interlayer insulation film will now be explained with reference to the accompanying drawings. FIG. 1A through FIG. 3B are cross sections showing the step-by-step sequence of a via first process, which is one embodiment of the conventional damascene process.
Initially, as shown in FIG. 1A, a first etching stopper film 7 to be used as an etching stopper for a via hole by preventing diffusion of Cu, a first interlayer insulation film 8 made of SiO2, a second etching stopper film 9 to be used as an etching stopper for a wiring trench pattern, and a second interlayer insulation film 18 of a low dielectric film, such as hydrogen silsesquioxane (hereinafter, abbreviated to HSQ) and methyl silsesquioxane (hereinafter, abbreviated to MSQ), are deposited sequentially from bottom to top on a substrate 2 in which a lower layer wiring 6 made of Cu has been formed. Subsequently, after a first reflection preventing film 11a is formed on the second interlayer insulation film 18, photoresist is applied thereon, which is subjected to exposure and development. A first resist pattern 12a to be used to form a via hole 3 is thereby formed.
Then, as shown in FIG. 1B, the first reflection preventing film 11a, the second interlayer insulation film 18, the second etching stopper film 9, and the first interlayer insulation film 8 are etched away sequentially through a known dry etching technique, using the first resist pattern 12a as a mask. A via hole 3 penetrating through these films is thereby formed.
Then, after the first resist pattern 12a and the first reflection preventing film 11a are removed, as shown in FIG. 1C, a second reflection preventing film 11b is formed and then photoresist is applied thereon, which is subjected to exposure and development. A second resist pattern 12b to be used to form a wiring trench pattern through etching is thereby formed. Subsequently, the second reflection preventing film 11b and the second interlayer insulation film 18 are etched away sequentially through a known dry etching technique, and a wiring trench pattern 13 is thereby formed (see FIG. 2A).
Then, as shown in FIG. 2B, the first etching stopper film 7 atop the lower layer wiring 6 is removed, after which, as shown in FIG. 2C, a barrier metal 4 to be used as a base layer for a wiring material is formed. Then, a wiring material 5, such as Cu, is embedded in the interiors of the wiring trench pattern 13 and the via hole 3, and the surface thereof is planarized through CMP (see FIG. 3A and FIG. 3B). A dual damascene structure is thus obtained.
In the conventional damascene process described above, when HSQ is used as the second interlayer insulation film 18, because HQS is an inorganic low dielectric film, it adheres well to a barrier metal, a silicon oxide film, and a silicon nitride film, which are also made of inorganic materials, and there occurs no problem that these inorganic materials are separated at the HSQ interface.
However, when a low dielectric film having a bond of Si and a group made of organic constituents, such as MSQ, is used as the second interlayer insulation film 18, it does not adhere well to an inorganic material, particularly, a barrier metal, and as shown in FIG. 3B, the barrier metal is separated from an MSQ-based low dielectric film during CMP, which gives rise to a problematic scratch 21 on the surface of the MSQ-based low dielectric film, or stress caused by the multi-level interconnection gives rise to problematic film separation 20 at the barrier metal/MSQ interface having poor adhesion. It should be noted, however, that the MSQ-based low dielectric film has a lower dielectric constant than HSQ, and is therefore expected as a promising next-generation interlayer film, which increases the importance of solving the adhesion problem at the interface between the MSQ-based low dielectric film and the barrier metal.
The reason why HSQ and MSQ have different adhesion to the barrier metal 4 as described above is attributed to the difference as follows: HSQ has a structure in which oxygen and hydrogen are bonded to silicon atoms, whereas MSQ contains organic constituents having a large molecular structure, such as a methyl group, in order to lower a dielectric constant, and the organic constituents at the MSQ interface interfere with bonding of Si and the barrier metal 4, such as tantalum (Ta) and tantalum nitride (TaN).
In order to prevent such unwanted separation, there has been discussed a structure that protects the groove sidewall after the groove is formed. For example, Japanese Patent Laid-Open Publication No. Hei. 10-284600 discloses a method of protecting the sidewall by providing a Si3N4 or SiO2 sidewall to a groove pattern formed in the low dielectric interlayer film. This method, however, cannot avoid an increase in dielectric constant when a thick film is formed, and deterioration in adhesion associated with a pin-hole when a thin film is formed.
Also, in order to prevent separation due to poor adhesion as described above, there has been discussed a method of improving adhesion by applying various surface treatments to the surface of MSQ after it is deposited. For example, during the fabrication sequence of a semiconductor device, cleaning through sputtering using an Ar gas is performed in many steps as needed, and Ar sputtering is performed to clean the surface of the lower layer wiring 6 at the bottom of the via hole 3 after the wiring trench pattern 13 is formed and before the barrier metal 4 is deposited. However, because merely a sputtered material is etched away through Ar sputtering, it proves to be ineffective in reforming the MSQ surface.
Also, there has been discussed a method of performing an ozone treatment, a UV ozone treatment, or an oxygen plasma treatment after MSQ is deposited, and Japanese Patent Laid-Open Publication No. 2001-223269 discloses a method of reforming the surface of the interlayer insulation film to be a silicon oxide film or a silicon dioxide film containing excessive silicon through irradiation of a charged beam of an ionized oxygen gas. This method, however, has a problem that water comes into the film and a dielectric constant of the insulation film is increased; moreover, the surface of the film is made rough and a residue is left thereon.
As has been described, it is essential to use a low dielectric film containing organic constituents, such as MSQ, as an interlayer insulation film to reduce an interconnect capacitance. However, the reliability reduced by poor adhesion of the low dielectric film to an inorganic material, particularly, a barrier metal, poses a serious problem, and there has been a need to develop a structure capable of increasing adhesion of the low dielectric film to the barrier metal, and a process capable of reforming the surface of the low dielectric film. This problem is not limited to the via first dual damascene process described above, and can occur in any other damascene process, such as a dual hard mask process and a single damascene process, as well as in any other process using a low dielectric film having a bond of Si and a group made of organic constituents.